As an instance of the rv_continuous class, halfnorm object inherits from it
a collection of generic methods (see below for the full list),
and completes them with details specific for this particular distribution.

The probability density above is defined in the “standardized” form. To shift
and/or scale the distribution use the loc and scale parameters.
Specifically, halfnorm.pdf(x,loc,scale) is identically
equivalent to halfnorm.pdf(y)/scale with
y=(x-loc)/scale.